Question

A shiny brown coloured element „X‟ on heating in air becomes black in colour . Name the

element „x‟ and the black coloured compound formed.​

Answer 1

Answer:

Since the oxide turns red litmus blue, therefore X is a metal because it is an alkaline oxide.

Most of the metals form respective metal oxides when react with oxygen.

Metal + Oxygen → metal oxide

Examples: (1) Reaction of potassium with oxygen:- Potassium metal forms potassium oxide when reacts with oxygen.

4k +O²-->2k²O

(2) Reaction of sodium with oxygen:- Sodium metal forms sodium oxide when reacts with oxygen.

4Na+O²-->2Na²O

Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis. Sodium oxide and potassium oxide dissolve in water to produce alkalis.

Na²O(s)+H²O(1)-->2NaOH(aq)